After microvascular decompression of the trigeminal nerve for relief of tic douloureux, about 70% of patients with a positive history of cold sores develop herpes lesions with onsets 2-5 days after surgery. We will administer interferon for five days, commencing the day prior to surgery, to 20 patients per year in order to modify the disease or reduce its frequency. Interferon in serum and throat washes will be assayed. A control group will receive a placebo. The patients, and others including those undergoing VIIth nerve surgery for hemi -facial spasm will be followed clinically, virologically and immunologically. The purpose of this phase of the study is to examine events occurring between the time of stimulus (surgery) and the appearance of overt lesions. This early phase of the pathogenesis of recurrent herpes is not usually available to investigators. We will ascertain the time of appearance of herpes virus in the oropharynx, (we commonly find the virus in throat washes), look, by fluourescent antibody methods, for the appearance and location of cells containing viral antigen in this site and follow humoral and cell mediated immunity to herpes virus.